This application is entitled to the benefit of and incorporates by reference essential subject matter disclosed in Japanese Patent Application No. 2001-316818 filed Oct. 15, 2001.
1. Field of the Invention
The present invention relates to a controller for an exhaust brake device which is combined with a power transmission device provided with a fluid coupling for transmitting the driving force of an engine to a gearbox, and a lock-up clutch for disengaging and engaging this fluid coupling, mechanically, and more particularly, it relates to a controller for an exhaust brake device which permits the exhaust brake device to be used in practice, even at low vehicle speed.
2. Description of the Related Art
An exhaust brake device used as a supplementary brake in a large vehicle, or the like, is principally constituted by an exhaust shutter provided in the exhaust path of the engine, a braking force being applied by actuating and closing the exhaust shutter so as to close the exhaust path.
Normally, in an manual transmission vehicle, an exhaust brake is used with the clutch in a fully engaged state and the accelerator in an non-pressed state (for example, in a state where the vehicle is descending a long downhill gradient).
In an automatic transmission vehicle which transmits the driving force of the engine to the gearbox by means of a fluid coupling, in cases where the lock-up clutch which mechanically disengages and engages the input and output sides of the fluid coupling is in a disengaged state, then even if the exhaust brake device is operated, slipping will occur in the fluid coupling, and no braking force will be obtained.
In particular, since the automatic transmission of an automatic transmission vehicle changes gear frequently at low speed, in practice, it is not possible to engage the lock-up clutch. In other words, if the lock-up clutch is engaged at low speed, then it is necessary to disengage and reengage the lock-up clutch each time the gear is changed, thereby impairing the sensation transmitted to the driver, and hence the lock-up clutch has to be engaged once the vehicle speed has been raised to a relative degree (in general, a high sensation of gear changing is required in automatic transmission vehicles).
From the foregoing, in an automatic transmission vehicle, the lock-up clutch has been engaged at medium speeds (for example, 40 km/h). Therefore, at low speed (for example, below 40 km/h), a problem arises in that no braking force is obtained even if the exhaust brake device is activated.
Moreover, whilst it is necessary to close the accelerator completely in order to activate the exhaust brake, in an automatic transmission vehicle, after starting off, an accelerating operation which reciprocates the braking is performed, namely, the gear is shifted up whilst releasing the accelerator, when the vehicle is accelerating at low speed, and therefore, it has not conventionally been possible to use an exhaust brake at low speed.
However, if the exhaust brake device is operated in a semi-compulsory manner at a low vehicle speed where the lock-up clutch is disengaged, in spite of the foregoing, then although the indicator panel will indicate to the driver that the exhaust brake is operating, no exhaust braking force will actually be obtained, and hence there will be a disparity between the driver""s perceptions and the operational indications.
Therefore, it is an object of the present invention to resolve the aforementioned problems, by providing a controller for an exhaust brake device whereby the exhaust brake device can be used in practice at low vehicle speeds.
In order to achieve the aforementioned object, the present invention is a controller for an exhaust brake device combined with a power transmission device provided with a fluid coupling connected to the output shaft of an engine, a friction-type gear change clutch interposed between said fluid coupling and a gearbox, and a lock-up clutch provided in said fluid coupling for mechanically disengaging and engaging the input and output side of said fluid coupling; comprising: an electronic control unit for controlling the engagement and disengagement of said friction-type gear change clutch, the engagement and disengagement of said lock-up clutch, and the operation of said exhaust brake device; wherein said electronic control unit: causes said lock-up clutch to engage when the vehicle speed is at or above a prescribed vehicle speed at which the engine will not stall, after the vehicle has started off; causes said friction-type gear change clutch to disengage and engage whilst said lock-up clutch remains engaged, when changing gear in said gearbox; and permits operation of said exhaust brake device in the range of engagement of said lock-up clutch.
According to this composition, after start up, the lock-up clutch is engaged, and gear changing in the gearbox is performed by disengaging and engaging a friction-type gear switch, as in an manual transmission vehicle, and therefore, the lock-up clutch can be engaged and the exhaust brake device can be used, at low vehicle speeds Moreover, since operation of the exhaust brake device is only permitted when the lock-up clutch is engaged, there is no disparity between the operational indications displayed for the exhaust brake device and the perceptions of the driver.
Furthermore, an input rotation sensor for detecting the number of revolutions of the input shaft of the gearbox may also be provided, the electronic control unit causing said lock-up clutch to engage when the number of revolutions of the input shaft detected by the input shaft rotation sensor exceeds a prescribed value.
Furthermore, the prescribed value of the number of revolutions of the input shaft may be set respectively for each gear level of the gearbox.